1. Field of the Invention
The present invention relates to an image sensing apparatus and an exposure control method, and more particularly, to an image sensing apparatus capable of detecting an object from a sensed image, and an exposure control method therefore.
2. Description of the Related Art
Conventionally, in a digital camera, there is an image sensing apparatus equipped with an automatic exposure control function that determines exposure automatically based on image data obtained by image sensing.
As photometric methods carried out for the purpose of automatic exposure control, there is, for example, evaluative photometry carried out by taking the entire frame into consideration, as well as multi-division photometry, in which a photometric area within the frame is divided into a plurality of blocks and photometry carried out in blocks. Besides these methods, there is center-weighted photometry, in which photometry is carried out with emphasis on the center portion of the frame, as well as spot photometry, in which photometry is carried out only for an arbitrary range of the center portion of the frame.
In addition, in order to get the luminance correct for a main object, there are apparatuses in which the user specifies the area in which the main object is present and the apparatus adjusts the exposure to match the specified area. Further, a camera that automatically detects, for example, a face as the main object by a technique such as shape analysis from image data obtained by image sensing and carries out exposure control so that the detected face is properly exposed has been proposed (see, for example, Japanese Patent Laid-Open No. 2003-107555). Such a camera brightens the entire frame if the face is underexposed even though the luminance of the frame overall is proper, and darkens the frame overall if the face is overexposed (see FIG. 7). Consequently, image sensing such that the luminance of the main object is proper no matter what the scene can be carried out.
However, with the method disclosed in Japanese Patent Laid-Open No. 2003-107555, in attempting to control the exposure so that the luminance of the detected face is proper, it sometimes happens that the background becomes overexposed or underexposed even though the luminance of the face is correct (see, for example, FIG. 8). In such cases, the image is not properly exposed when looked at as a whole.
Although image processing of such improperly exposed images to adjust the brightness is also conventionally done, in general, image contrast after processing is worse in overexposed images than in underexposed images, resulting in many cases in images that appear to be blurred.